One in five has a mutation that provides ‘superior resilience’ to chilly temperatures
Why some people never feel the cold: One in five has a mutation that provides ‘superior resilience’ to chilly temperatures, study reveals
- The α-actinin-3 protein, found in ‘fast-twitch fibres’, is absent in 1 in 5 people
- Volunteers sat down in cold 14°C water while scientists examined their muscles
- 70 per cent of those without the protein could hold their temperature in the cold
- Just 3 out of 10 of those that had the same protein were able to maintain their temperature when scientists had them immersed in cold water
A fifth of the world’s population has a ‘superior resilience’ to colder temperatures thanks to a genetic mutation, allowing them to never feel the cold, study reveals.
Researchers at Karolinska Institutet in Sweden had 32 healthy men aged 18 to 40 sit in 14 degrees Celsius water until their body temperature dropped to 35.5C.
They then measured the muscle electrical activity and took muscle biopsies of the volunteers to study their protein content and fibre composition.
The α-actinin-3 Protein, found in ‘fast twitch fibres’ inside the muscles, is absent in about 20% of people and its absence makes them better and keeping warm.
This is because the muscles of people without the protein contain a greater proportion of slow-twitch fibres, which allows them to maintain their body temperature in cold environments in a more energy-efficient way.
Researchers at Karolinska Institutet in Sweden had 32 healthy men aged 18 to 40 sit in 14 degrees Celsius water until their body temperature dropped to 35.5C. Stock image
The team behind the study believe this genetic variant may have protected modern humans against the cold as they migrated out of Africa over 50,000 years ago.
Based on their study, the team believe that about 1.5 billion people worldwide will carry the variant today – increasing their tolerance of colder climates.
Co-senior author Håkan Westerblad said: ‘Our study shows an improved cold tolerance in people lacking α-actinin-3, which would have been an evolutionary survival advantage when moving to colder climates.
‘Our study also highlights the great importance of skeletal muscle as a heat generator in humans.’
The findings suggest this is because the deficiency of α-actinin-3 boosts cold tolerance by increasing their muscle tone and leads to more slow-twitch muscles.
When immersed in cold water during an experiment, people with the variant had an increase in muscle tone rather than shivering.
The loss of α-actinin-3 is caused by the loss-of-function (LOF) variant of the ACTN3 gene and became more common as more humans moved to colder environments.
Around 1.5 billion people worldwide carry the ACTN3 LOF variant today and therefore lack α-actinin-3.
Although this protein deficiency is not linked with muscle disease, it does impair performance during power and sprint activities.
The change became more prominent as humans began to move into cooler climates – which researchers use as their argument why it may improve cold tolerance.
To test this idea, the team immersed 42 healthy 18 to 40-year-old men with either the LOF variant or functioning ACTN3 in 14 °C water.
The men remained in the water for 20-minute periods, broken up by ten minute pauses in room-temperature air.
Cold-water exposure was continued until the rectal temperature reached 35.5 degrees, or for a total of two hours plus fifty minutes of pauses.
Of those men that had the genetic variant 7 out of 10 where are able to maintain their body temperature above 35.5°C for the complete cold water exposure period.
However, only three and 10 of those without the variant were able to do so.
The muscles of people without the protein contain a greater proportion of slow-twitch fibres, which allows them to maintain their body temperature in cold environments in a more energy-efficient way
On average, loss of α-actinin-3 resulted in half the rate of temperature decline in the rectum and on the calf muscle.
People with the variant also showed a shift toward more slow-twitch muscle fibres, causing an increase in muscle tone rather than shivering during immersion.
By contrast, individuals without the variant had more fast-twitch muscle fibres, which doubled the rate of high-intensity bursting activity.
The superior cold resistance of people with the variant was not accompanied by an increase in energy consumption.
This suggests that the continuous, low-intensity activation of slow-twitch muscle fibres is an energetically effective way to generate heat.
Results in mice showed that α-actinin-3 deficiency does not increase cold-induced brown fat tissue, which generates heat in hibernating mammals and human infants.
Co-senior study author Professor Marius Brazaitis, of Lithuanian Sports University in Kaunas, Lithuania, added: ‘Although there are many avenues for future investigation, our results increase our understanding of evolutionary aspects of human migration.
‘While the energetically efficient heat generation in people lacking α-actinin-3 would have been an advantage when moving to colder climates, it might actually be a disadvantage in modern societies,’ he said.
Housing including Nico protection less important and as we’ve got relatively limited access to food such energy efficiency and our bodies can actually result in obesity Type II diabetes and other metabolic disorders, Brazaitis added.
For now, it remains uncertain whether the loss of α-actinin-3 affects brown fat tissue or cold tolerance of human infants, whose survival would have been an important factor during the human migration to colder environments.
While the variant may increase slow-twitch muscle fibres at birth, it is possible that this shift doesn’t occur until later in life.
Researchers add it is also not clear whether α-actinin-3 deficiency affects heat tolerance or responses to different types of athletic training.
The findings have been published in the American Journal of Human Genetics.
